Yes, however Romanov royal children (and some of the Russian nobility) often, as your above list shows, had British nannies from their earliest years. The parents of these children may have encouraged them to learn the basics of English words, expression and pronunciation from these servants.
Also, in Alexander III’s time and earlier, French was the language of Court life. The children might have grown up absorbing this and learned the basics of French while quite young.
None of this helps in your search for your forebear’s sister of course. However, as there appears to be sparse documentation that Charlotte was Governess to the Romanov royal children for any length of time, is it possible that for a short period she could have been a nursery governess to them but then left her employment with the royal household?
It seems odd to me that while some other English nannies and tutors are mentioned, albeit briefly, her name doesn’t seem to have appeared in any existing Romanov records as her family seems to have believed (been told) that she was a senior governess to the Tsar’s children.
Perhaps Charlotte suffered from intermittent bad health (heart problems) but gained employment with other Russian noble families as a nursery governess in the 1880s.
In any case, much good luck with your search.